A solar collector collects solar radiation to produce solar cell output voltage. One type of solar collector moves with the sun, to face toward the sun as the sun changes its position during a daylight period. The elevation angle of the sun changes as the sun ascends and descends, and the horizontal angle of the sun changes with the movement of the sun from horizon to horizon. A solar tracking system adjusts an elevation angle of the solar collector and adjusts a horizontal angle of the solar collector to correspond with changes in the sun's position throughout a daylight period.
Prior to the invention, solar tracking for a solar collector was mathematically calculated. A computer program was devised to produce solar tracking for different days of the year, and for different latitude and longitude positions. The computer program controlled drive motors that moved the solar collector in a manner to track the sun.
U.S. Pat. No. 4,628,142 discloses a solar tracking system that foregoes a computer program. The system includes a cable that lengthens and shortens to move a solar collector about a horizontal axis. The cable is attached to coils of shape memory alloys that absorb solar energy. When illuminated by the sun, the coils of shape memory alloys uncoil, which lengthen the cable. When shaded from the sun, the shape memory alloys form tighter coils, which shorten the cable.
U.S. Pat. No. 4,832,001 discloses a solar collector having two solar heated canisters containing Freon. The canisters are interconnected to exchange Freon from one canister to another. When both canisters are illuminated by the sun, they absorb solar energy to evaporate the Freon to a gaseous state. When one of the canisters is shaded from the sun, the Freon in the shaded canister condenses to a liquid state, making the shaded canister containing liquid Freon heavier than the illuminated canister containing gaseous Freon. The heavier weight moves the solar collector until both canisters become illuminated by the sun, which evaporates the Freon and equalizes the canister weights.